# Cooling All External Degrees of Freedom of Optically Trapped Chromium Atoms Using Gray Molasses

## TL;DR

This paper presents a method combining gray molasses and harmonic trap evolution to cool all external degrees of freedom of chromium atoms, significantly increasing phase-space density for quantum regime experiments.

## Contribution

The study introduces a novel cooling scheme that effectively cools all external degrees of freedom of trapped chromium atoms using gray molasses combined with trap evolution.

## Key findings

- Phase-space density increased by a factor of 250
- Achieved a final PSD of about 1.7×10^-3
- Gray molasses effective in optical dipole traps

## Abstract

We report on a scheme to cool and compress trapped clouds of highly magnetic 52Cr atoms. This scheme combines sequences of gray molasses, which freeze the velocity distribution, and free evolutions in the (close to) harmonic trap, which periodically exchange the spatial and velocity degrees of freedom. Taken together, the successive gray molasses pulses cool all external degrees of freedom, which leads to an increase of the phase-space density (PSD) by a factor of about 250, allowing to reach a high final PSD of about 1.7*10^-3. These experiments are performed within an optical dipole trap, in which gray molasses work equally well as in free space. The obtained samples are then an ideal starting point for the evaporation stage aiming at the quantum regime.